Research – Investigation into an outbreak of Shiga toxin producing Escherichia coli (STEC) O157 PT 21/28 Stx2 in England, August 2017 – Raw Pet Foods


In August 2017, a cluster of 4 cases infected with genetically related strains of STEC O157 was identified. The strains possessed the stx2a toxin subtype, a toxin type known to be associated with more severe disease and the development of Haemolytic Ureamic Syndrome (HUS), a serious complication of this infection, predominantly affecting the kidneys. One case had died following development of HUS.

A multi-agency investigation was undertaken which included re-interviewing cases and the sampling and testing of implicated products. Interviews indicated that 3 of the cases had been exposed to dogs fed on a raw meat based diet), specifically, tripe. In 2 cases, the tripe has been purchased from the same supplier.

While one case was not linked to raw pet food, as cattle and sheep are the main reservoir of STEC in the UK, exposure to the same strain of STEC may have occurred through a different route. This may be indirect or direct exposure to the infected animals which entered the pet feed supply chain for example. Alternatively, the case may have been exposed to an animal fed a raw meat based diet without being aware of, or being able to recall that exposure.

Sampling and microbiological screening of raw pet food was undertaken and indicated the presence of STEC in the products. STEC was isolated from one sample of raw tripe but was different to the strain causing illness in the humans. Nevertheless, isolation of STEC did provide evidence for microbiological contamination of tripe and its pathogenic risk to human health and that it was a plausible transmission route in this outbreak. This adds to the evidence of raw pet food as a risk factor for zoonotic transmission of GI pathogens, which is already relatively widely accepted for salmonella, listeria and campylobacter.

Feeding raw meat based diet to companion animals has recently increased in popularity due to both increasing availability and beliefs that they provide health benefits to animals. Although still rare, an increase in STEC cases reporting exposure to raw meat based diet ’s was detected in 2017. There has also been an increased frequency of raw pet food incidents in 2017, suggesting an increasing trend in potential risk to humans from raw pet food. IMT concluded that the best approach to reduce the risk of infection is to improve awareness of risk and promote good hygiene practices amongst the public when handling raw pet food.


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